3/15/2006

Pessimistic induction + incommensurability = instrumentalism?

One popular formulation of Scientific Realism is: Mature scientific theories are (approximately) true.
One of the two main arguments against this claim is the so-called 'Pessimistic (Meta-)induction,' which is a very simple inductive argument from the history of science: Most (or even almost all) previously accepted, (apparently) mature scientific theories have been false -- even ones that were very predictively successful. Ptolemy's theory yielded very good predictions, but I think most people would shy away from saying 'It is approximately true that the Sun, other planets, and stars all rotate around a completely stationary Earth. So, since most previous scientific theories over the past centuries turned out to be false, our current theories will also probably turn out to be false. (There are many more niceties which I won't delve into here; an updated and sophisticated version of this kind of argument has been run by P. Kyle Stanford over the last few years.)

The kind of anti-realism suggested by the above argument is that the fundamental laws and claims of our scientific theories are (probably) false. But we could conceivably read the history of science differently. Many fundamental or revolutionary changes in science generate what Kuhn calls 'incommensurability': the fundamental worldview of the new theory is in some sense incompatible with that of the older theory -- the changes from the classical theories of space, time, and matter to the relativistic and quantum theories are supposed to be examples of such changes. Communication breaks down (in places) across the two worldviews, so that each side cannot fully understand what the other claims.

Cases of incommensurability (if any exist) could result in each side thinking the other is speaking incomprehensibly(or something like it), not merely that what the other side is saying is false in an ordinary, everyday way. An example from the transition from Newtonian to (special) relativistic mechanics may illustrate this: Suppose a Newtonian says 'The absolute velocity of particle p is 100 meters per second.' The relativistic physicist would (if she is a Strawsonian instead of a Russellian about definite descriptions) say such a sentence is neither true nor false -- because there is no such thing as absolute velocity. [A Russellian would judge it false.] If she merely said "That's false," the Newtonian physicist would (presumably) interpret that comment as 'Oh, she thinks p has some other absolute velocity besides 100 m/s; perhaps I should go back and re-measure.' To put the point in philosophical jargon: presuppositions differ between pre- and post-revolutionary science, and so the later science will view some claims of the earlier group as exhibiting presupposition failure, and therefore as lacking a truth-value, like the absolute velocity claim above. (Def.: A presupposes B = If B is false, then A is neither true nor false)

This leads us to a different kind of pessimistic induction: (many of) the fundamental theoretical claims of our current sciences probably lack a truth-value altogether, since past theories (such as Newtonian mechanics) have that feature. (If you want to call claims lacking truth-values 'meaningless,' feel free, but it is not necessary.) This is hard-core instrumentalism, a very unpopular view today; most modern anti-realists, following van Fraassen, think that all our scientific discourse is truth-valued (though we should be agnostic about the truth-value of claims about unobservable entities and processes). But this instrumentalism seems to be a natural outcome of (1) taking the graveyard of historical scientific theories seriously, (2) believing there is something like Kuhnian incommensurability, and (3) holding that incommensurability involves presupposition failure. And none of those three strike me as crazy.

Disclaimer: This argument has probably been suggested before, but I cannot recall seeing it anywhere.

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13 Comments:

At 15/3/06, Blogger "Q" the Enchanter said...

Phlogiston is an interesting case, but I can't think of a single successful prediction that came of that hypothesis. (Then again, I have no relevant expertise.) I know Kuhnians will say that "explained" burning, e.g., but why not just say phlogiston was merely an hypothesis that, once tested, called for a different hypothesis?

 
At 15/3/06, Blogger "Q" the Enchanter said...

"...will say that phlogiston "explained" burning," that is.

 
At 15/3/06, Blogger GF-A said...

Q--

Some people resist the pessimistic meta-induction on the grounds I take you to be suggesting for phlogiston: the theories (or their parts) that end up being scrapped entirely are not paradigmatically good scientific theories, because (as you suggest) they generate no new predictions, or because they lack some other theoretical virtue that we think good science should have. And because our modern theories do make new predictions etc., they should not be put in the same boat with phlogiston and the rest.

I can't quite tell what you make of the rest of the post, though. The point I was trying to make in the original post, and which I can't tell whether you accept or not, is that we might want to regard the sentence
"Wood contains more phlogiston than lead does"
not as false but rather as being neither true nor false -- because if we today declare this sentence false, then (on one non-crazy semantics) we modern anti-phlogistonites are committed to lead's phlogiston content being greater than or equal to the phlogiston-content of wood. But modern anti-phlogistonites don't believe that.

 
At 15/3/06, Blogger "Q" the Enchanter said...

I have no relevant expertise, so my opinion is worth what your paying for it. That said, I'm always inclined to answer this type of question with a "no--because" clause ("Is the present King of France bald?" "No--there is no King of France.")

If you like, propositions like these are "p-false"--false in respect of some faulty presupposition. This seems a sensible way of approaching statements like "The tree's phlogiston was liberated," "Thursdays are green" and "God is a unicorn," because it simply isn't the case that trees liberate phlogiston or that Thursdays are green or that God is a unicorn.

I don't know how productive making a place for p-properties or p-relations in predicate logic would be, but it does seem to account for linguistic usage.

 
At 15/3/06, Anonymous Protagoras said...

Phlogiston theory explained why metals have such similar properties. According to the theory, all metals have a high phlogiston content. The fact that metals can generally be oxidized (to use the terminology of modern theory; the phlogiston chemists would of course have said metals can be made to release their phlogiston) lends further credibility to this account.

Oxygen chemistry had no comparable account of the similar properties of metals.

 
At 15/3/06, Blogger "Q" the Enchanter said...

Protagoras, in the accounts I've read, phlogiston theory is said to have encompassed all flammable materials (inc., e.g., wood). Is that incorrect?

 
At 15/3/06, Blogger Kenny said...

I think the third premise in your argument is the one that I'd contest. Incommensurability may sometimes involve presupposition failure, but my crude understanding was more that it's a failure of translation. Thus, the meaninglessness of old theories is somehow language-relative. I don't know if there are any cases in the history of science where theory A was rejected in favor of theory B, making proposition P seem now meaningless, but when B was rejected in favor of C, P all of a sudden had a meaning again. If that has happened, then we no longer have such a drastic pessimistic metainduction as you suggest.

 
At 16/3/06, Blogger GF-A said...

For Mr. Q --

I am no phlogiston expert either, but I just found a brief but informative selection from Jospeh Priestley (supposedly the last advocate of phlogiston) here.

I know that there are Russellians out there, and folks who want to hold on to bivalence (= every sentence is either true or false and not both) at all costs. Those folks will not accept the original argument. But this idea of p-falsity is interesting and strange to me. Is p-falsity a third truth value? Does it behave truth-functionally? Is there p-truth? And what do you mean by 'p-relation' or 'p-property'? I think of presupposition as a fundamentally linguistic affair, and of properties and relations as extra-linguistic.

Kenny--

1. I think you're right about untranslatability. Your comment made me realize that I was assuming that if a sentence S of language L1 is untranslatable into L2, then S is neither true nor false in L2. But that tacit assumption seems fine to me.

2. The 'reversal' issue you mention comes up in the 'standard' pessimistic metainduction too -- the science of optics has gone back and forth on the question of whether light is corpuscular or wavey. (Current answer: both!) So it seems like your point doen't apply any more to the 'instrumentalist' metainduction of the post than to the 'traditional' metainduction.

** And why is it called a META-induction?? Doesn't it have the usual form of an inductive argument?

 
At 19/3/06, Blogger Kenny said...

Isn't it because it's an induction on the relative success of our inductive practices? Induction has led us to make false conclusions every time in the past, so it probably will keep doing so. Which I guess is the converse of Hume's optimistic meta-induction - the reason we believe the future will be like the past is because it always has been before. I suppose using induction to undermine induction is not as circular as using induction to support induction.

 
At 19/3/06, Blogger Quirinius_Quine said...

Two things come to mind: First, how do we know that the disgarded theories are really false? If we cannot trust science to establish the truth of a theory, why should we trust it to reveal the falsity of a theory? To me it seems that if we can trust it to establish falsity, we can trust it (eventually) to reveal the truth, which descredits your conclusion. Conversly, if we cannot trust science to falsify theories, from where can you get support for your premise that past scientific theories are false? Of course conflicting theories regarding the same phenomenon cannot all be true, but how could we trust science to falsify any particular theory?

Regarding incommensurability: I'm not sure presupposition failure gets us there. What if the einsteinian physicist tells the newtonian one that there simply is no such thing as absolute velocity? Even granting that the newtonian's statement regarding velocity presupposed the existence absolute velocity, I don't see how a categorical denial on the part of the einsteinian would violate any presuppositions. E.g., even if "The present king of france is bald" is neither true nor false, "there is no present king of france" need not be regarded as truth-valueless. So what would prevent the newtonian from understanding the einsteinian's denial that there is such a thing as absolute velocity? If it could be understood, presupposition failure might be a real but relatively harmless phenomenon.

 
At 20/3/06, Blogger "Q" the Enchanter said...

Greg, thanks for the interesting link.

On this p-falsity idea, my (very inchoate) thought is that a sentence S is p-false if and only if (1) it is not the case that S (2) because S presupposes a condition that does not obtain.

The presupposition in question could be either referential or predicative. I mention this distinction because it seems to make a difference regarding negation. E.g., "TPKF is bald" and "TPFK is not bald" are both p-false, whereas "Thursday is green" and "Thursday is not green" are respectively false and true (or, if you like, p-false and p-true).

It's really beyond my ken to work out the metalogical implications of this sort of approach (I've lost all my formal systems chops, such as they were), but I'll take a shot at answering your follow-up questions.

I would say p-falsity operates as a way of carving out exceptions to the law of excluded middle, but is nonetheless parasitic on the standard notion of truth. So on this hand it wouldn't appear to be a "third truth value."

On the other hand, p-falsity doesn't seem to be "truth-functional" in the normal sense, since the success of reference and/or predication needs to be known in order to determine the truth of the proposition. (So maybe this account is after the fashion of Russellian description, relying on the idea of a suppressed existential proposition, along with the idea of a suppressed, second-order predicative proposition.)

A "p-property" (or "p-relation") would be a property (or relation) that either has no instantiator or else cannot be predicated of some defined type of instantiator. (E.g., omnipotence has no instantiator, and green can't be predicated of things like Thursdays. BTW, I find the latter example interesting because it runs counter to the general "rule" that both falsely-presupposing sentences and their negations are false.)

I'm not sure if any of this speaks to your last point about the (extra)linguistic nature of presupposition. In any case, maybe you'll be sufficiently armed to decide whether the whole idea is duplicative of some extant theory, or otherwise just plain incoherent. On the other hand, perhaps you will work it out and thereby solve all the main problems in philosophy of language (including Moore's paradox, of course). In which case I want credit.

 
At 27/5/06, Anonymous Anonymous said...

The extreme instrumentalist does believe, after all, that some entities really do exist in the world: namely, mind and the world (or variants like mind/matter, physical/mental, real/unreal, thoeretical/actual and the like) ---and the mutually exclusive distinction between them. But I can't fathom how it can be right to at once hold that you cannot know it to be true that the world is the same as what you think it is-- without at the same time holding that this state of affairs (that you cannot know that the world is the same as you think it is)-- is true of the world and that you know it is. "oh it's just theoretical" says the instrumentalist, but this doesn't help because he is saying it is true of the world -- an actual state of affairs that it is theoretical and that he knows it is.
The instrumentalist may further say: "I believe all these entities and states of affairs that science thinks up are just good ways to get results we like though we can't know if these entities and states of affairs are the world or not-" but the instrumentalist does not say further: " but because I don't think that we can know if our words and concepts really state the actual state of the world---I must admit I am contradicting myself and so I withdraw my previous contention."
In other words the instrumentalist is a kind of realist who just differs from other realists in what he holds to be real and actual.
And what about the realist? If he maintains that the mind and the world are distinct then it seems we cannot we know about the world--there is no point at which the two entities are identical. so how can the realist maintain that there is or isn't a world apart from the mind--that mind and world are distinct? If he gives up the distinction then he loses the distinction between mind and world which makes knowing distinct from just positing a state of affairs. If he keeps the distinction he can't say we can know.
Well then, suppose the realist brings in that entity, the proposition, to bridge the gap between the mind and the world. But same problem: If a proposition is posited as the object of knowledge, how do we know there is such an entity as a proposition in the world ( or a correspondence or a representation and so on) if we can't know the world? How do we know the proposition somehow captures the world? It seems we cannot if it is assumed that the world is separate from the proposition. Essentially the realist says "just trust me" that the proposition does somehow heal the gap. Snake oil. Even a desparate realist would not say "oh we think a proposition is just a hypothetical thing that is useful" -- that would make him some kind of instrumentalist. He must maintain that a proposition really does-- in actuality, in reality--- exist and that the world is knowable thereby-- But how can we know this is the case if there is a gap between the mind and the proposition and the proposition and the world? It just compounds the inaccessability.
So what is the solution? Well, there really isn't one---if both the instrumentalist and the realist insist that there are these entities-- mind/world etc.-- which do not overlap and share no point of identity then both positions are untenable from my point of view.
But I would be naive to think that there is no one out there to posit another possibility that would make them tenable to somebody.
I think though that as long as the distinctions of mind/ world etc. are made, they will operate like premises. Once you make the gap and refuse to abandon it or substitute another idea-- just so long will you be preoccupied with issues arising from the premise of that gap. You will spend all your time trying to reconcile two things you, from the get go, hold mutually exclusive. Now I think it is fun to seek out the implications of the gap-- to describe what may follow from the premises--to find out the ins and outs -but to hold that the premises are inviolable while trying to violate them as I see the instrumentalist and the realist doing-- seems to me like being caught in a kind of philosophical backwater, no matter how well it builds analytical skill.
I want pholosophy to break out of the pattern. One position could be that there are different positions and one of them is that there is one truth and we must search for it-- the one set of indubitable statements or propositions---is out there and we must discover them. It is in this context (no I am not a contextualist) that holding fast to the mind/world split would be consistent. Otherwise, I say there are lots of points of view and no one of them is necessity because there is not one that cannot be ignored. So, the mind /world gap does not necessarily have to obtain.
And when it does not onbtain I think philosophy will be better for it.
I know I have simplified the positions of realist and instrumentalist. If my account of positions is flawed I maintain that my objections still generally apply. Or not.

 
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